Coating composition

ABSTRACT

A coating composition comprising: 
     (A) 100 parts by weight of a vinyl polymer having on the main polymer chain end or a side chain thereof at least one silyl group containing a silicon atom to which a hydrolyzable group is linked, per one polymer molecule, the main chain of the vinyl polymer consisting essentially of a polymer of a vinyl monomer, 
     (B) 0 to 10 parts by weight of a curing catalyst, 
     (C) 0 to 10 parts by weight of a hydrolyzable ester compound, and 
     (D) 0.5 to 100 parts by weight of a dialkyl ester of dibasic acid having the formula (1): ##STR1## The coating composition of the present invention has excellent adhesion to under coats, and therefore it is suitable for use as automotive refinishing paints and industrial coatings.

BACKGROUND OF THE INVENTION

The present invention relates to a coating composition having improvedadhesion, and more particularly to a coating composition havingexcellent adhesion to under coats which is improved by using a dialkylester of dibasic acid as a solvent.

As a process for improving adhesion of a hydrolyzable silylgroup-containing vinyl copolymer to under coats, there have hithertobeen known a process wherein a polar group such as carboxyl group orhydroxyl group is introduced into a main chain of the vinyl copolymer, aprocess wherein an amine silane coupling agent or an epoxy-modifiedamine silane coupling agent is admixed with the vinyl copolymer, and thelike.

An object of the present invention is to provide a coating compositionhaving excellent adhesion to under coats.

This and other objects of the present invention will become apparentfrom the description hereinafter.

SUMMARY OF THE INVENTION

The present inventors have paid attention to solvents in solventcoatings, which is one of the essential components of solvent coatingsin addition to a main agent and additives, and studied the influence ofsolvents in solvent coatings using a hydrolyzable silyl group-containingvinyl copolymer on the adhesion to various under coats. As a result, ithas now been found that a dialkyl ester of dibasic acid has greatinfluence on the improvement of adhesion of solvent coatings to films ofthermoplastic resin coatings such as CAB-alkyd coating, straight acryliccoating and modified acrylic lacquer and thermoplastic resin coatingssuch as melamine alkyd coating and acrylic melamine coating.

In accordance with the present invention, there is provided a coatingcomposition comprising:

(A) 100 parts by weight of a vinyl polymer having on the main polymerchain end or a side chain thereof at least one silyl group containing asilicon atom to which a hydrolyzable group is linked, per one polymermolecule, the main chain of the vinyl polymer consisting essentially ofa polymer of a vinyl monomer,

(B) 0 to 10 parts by weight of a curing catalyst,

(C) 0 to 10 parts by weight of a hydrolyzable ester compound, and

(D) 0.5 to 100 parts by weight of a dialkyl ester of dibasic acid havingthe formula (1): ##STR2## wherein R¹ is a bivalent group having 1 to 10carbon atoms selected from the group consisting of an alkylene group, anarylene group and an aralkylene group, R² and R³ are the same ordifferent and each is an alkyl group having 1 to 4 carbon atoms, and nis an integer of 1 to 10.

DETAILED DESCRIPTION

A polymer of which the main chain consists essentially of a polymer of avinyl compound and which has on the polymer chain end or the side chainthereof at least one silicon atom combined with a hydrolyzable group perone polymer molecule (hereinafter referred to as "hydrolyzable silylgroup-containing vinyl polymer") is used in the present invention as acomponent (A). The hydrolyzable silyl group-containing vinyl polymersare prepared by copolymerizing a polymerizable organic silane with avinyl monomer. Examples of the polymerizable organic silanes are, forinstance, a hydrolyzable silyl group-containing vinyl monomer such asγ-methacryloyloxypropyltrimethoxysilane, vinyltrimethoxysilane orvinyltriethoxysilane, and the like. Examples of the vinyl monomers are,for instance, styrene, esters of acrylic or methacrylic acid such asmethyl acrylate or methacrylate, ethyl acrylate or methacrylate, butylacrylate or methacrylate, 2-ethylhexyl acrylate or methacrylate,tridecyl acrylate or methacrylate and stearyl acrylate or methacrylate;acrylamide, acrylonitrile, methacrylamide, N-methyloyl acrylamide ormethacrylamide, maleic anhydride, acrylic acid, methacrylic acid, avinyl monomer having hydroxyl group such as 2-hydroxyethyl acrylate ormethacrylate, and the like.

The copolymerization of the polymerizable organic silane with the vinylmonomer can be conducted in a usual solution polymerization manner. Amixture of the polymerizable organic silane, the vinyl monomers, aradical polymerization initiator and, for obtaining the silylgroup-containing vinyl polymer (A) having a molecular weight of 3,000 to50,000 if necessary, a chain transfer agent such as t-dodecylmercaptanis reacted at a temperature of 50° to 150° C. It is preferable to use,in the copolymerization, non-reactive solvents, e.g., hydrocarbons suchas toluene, xylene, n-hexane and cyclohexane, esters of acetic acid suchas methyl acetate and butyl acetate, alcohols such as methanol, ethanol,isopropanol and n-butanol, ethers such as methyl cellosolve and ethylcellosolve, and the like.

In the present invention, a curing catalyst as a component (B) may beused or not used. Examples of the curing catalysts are, for instance,organotin compounds such as dibutyl tin dilaurate, dibutyl tin maleate,dioctyl tin maleate and tin octoate; acidic phosphoric esters such asdibutyl phosphate, dioctyl phosphate, monobutyl phosphate and monooctylphosphate; amines such as butylamine and ethanolamine, organic acidssuch as maleic acid and p-toluenesulfonic acid, organic titanate such astetrabutyl titanate, organic aluminum compounds such astributoxyaluminum, and the like.

The curing catalyst is used in an amount of 0 to 10 parts by weight,preferably from 0 to 5 parts by weight, per 100 parts by weight of thehydrolyzable silyl group-containing vinyl polymer (A).

A hydrolyzable ester compound is used in the present invention as acomponent (C). Examples of the hydrolyzable ester compound are, forinstance, orthoformic esters such as methyl orthoformate and ethylorthoformate, orthoacetic esters such as methyl orthoacetate and ethylorthoacetate, hydrolyzable silicon compounds such asmethyltrimethoxysilane, methyltriethoxysilane, ethyl silicate, methylsilicate, γ-methacryloyloxypropyltrimethoxysilane, vinyltrimethoxysilaneand vinyltris(2-methoxyethoxy)silane, and the like. The hydrolyzableester compound (C) is used in order to stabilize the hydrolyzable silylgroup-containing vinyl polymer (A) and it may be added before or afterthe copolymerization of the hydrolyzable silyl group-containing vinylpolymer (A).

The hydrolyzable ester compound (C) is used in an amount of 0 to 10parts by weight, preferably from 0.5 to 10 parts by weight, per 100parts by weight of the hydrolyzable silyl group-containing vinyl polymer(A).

A dialkyl ester of dibasic acid used in the present invention as acomponent (D) has the formula (1): ##STR3## wherein R¹ is a bivalentgroup having 1 to 10 carbon atoms selected from the group consisting ofan alkylene group, an arylene group and an aralkylene group, R² and R³are the same or different and each is an alkyl group having 1 to 4carbon atoms, and n is an integer of 1 to 10.

Examples of the dialkyl esters of dibasic acid (D) are, for instance,dimethyl malonate, dimethyl succinate, dimethyl maleate, dimethylglutarate, dimethyl adipate, diethyl malonate, diethyl succinate, andthe like.

The dialkyl ester of dibasic acid (D) is used in an amount of 0.5 to 100parts by weight, preferably from 2 to 50 parts by weight, per 100 partsby weight of the hydrolyzable silyl group-containing vinyl polymer (A).When the amount of the dialkyl ester of dibasic acid (D) is less than0.5 parts by weight, the adhesion is lowered. On the other hand, whenthe amount is more than 100 parts by weight, the initial drying propertyis lowered.

The dialkyl ester of dibasic acid (D) may be added before or during thepolymerization of the hydrolyzable silyl group-containing vinyl polymer(A). Also, the ester (D) can be used as a solvent in the preparation ofthe vinyl polymer (A). Further the ester (D) can be used as a solvent ora diluent of solution coatings.

Although the reason why the dialkyl ester of dibasic acid (D) canimprove the adhesion of coatings is not made clear, it is consideredthat the dialkyl ester of dibasic acid can dissolve coated films ofunder coats.

As a solvent used in the coating composition of the present invention inaddition to the component (D), there can be used hydrocarbons such astoluene, xylene, hexane and an aromatic solvent commercially availableunder the tradename "Solvesso#100" made by Toa Nenryo Kogyo KabushikiKaisha, esters of acetic acid such as ethyl acetate, butyl acetate andisobutyl acetate, alcohols such as methanol, ethanol, isopropanol,n-buthanol and isobuthanol, ethers such as methyl cellosolve, ethylcellosolve, butyl cellosolve and ethyl cellosolve acetate, ketones suchas acetone, methyl ethyl ketone, methyl isobutyl ketone, diacetonealcohol, acetyl acetone and isophorone, and the like.

The coating composition comprising the components (A), (B), (C) and (D)of the present invention may contain or not contain a known agent forimproving adhesion. When using the agent for improving adhesion, therecan be used aminosilane compounds such as γ-aminopropyltrimethoxysilane,γ-aminopropyltriethoxysilane, N-β-aminopropyltrimethoxysilane andN-β-(aminoethyl)-aminopropyltriethoxysilane, and reaction products ofthe above-mentioned aminosilane compound and an epoxy compound. Examplesof the epoxy compounds are, for instance, epoxy silane compounds such asγ-glycidoxypropyltrimethoxysilane andβ-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, bisphenol A epoxy resins,epoxyurethane resins, novolak epoxy resins, and the like.

The composition of the present invention may further contain variouspigments, alkyd resins, cellulose resins such as cellulose acetate,butyrate and nitrocellulose, acrylic resins, and polyvinyl butyralresins, according to the use of the composition.

The coating composition of the present invention is suitable for use asautomotive refinishing paints, industrial coatings, and the like, sinceits adhesion is improved.

The present invention is more specifically described and explained bymeans of the following Examples in which all % and part are by weightunless otherwise noted. It is to be understood that the presentinvention is not limited to the Examples and various changes andmodifications may be made in the present invention without departingfrom the spirit and scope thereof.

REFERENCE EXAMPLE 1

To 200 g of xylene heated at 100° C. was added dropwise with stirringunder nitrogen gas for 5 hours a mixture of 100 g ofγ-methacryloyloxypropyltrimethoxysilane, 70 g of styrene, 100 g of butylacrylate,, 176 g of methyl methacrylate, 50 g of stearyl methacrylate, 4g of acrylamide and 27 g of azobisisobutyronitrile. A solution of 3 g ofazobisisobutyronitrile dissolved in 100 g of toluene was further addeddropwise to the system for 1 hour, and the polymerization was continuedfor 2 hours. To the obtained reaction mixture was added 36 g of xyleneto give a silyl group-containing vinyl copolymer in the form of asolution, having a solid content of 60%. The thus obtained copolymer hada number average molecular weight of 4,500 measured by gel permeationchromatography (hereinafter referred to as "GPC").

EXAMPLE 1

A straight acrylic coating (silver) was coated on a polished mild steelplate as a metallic base and the film was subjected to the setting atroom temperature for about 30 minutes [thickness of the dried film(metallic base layer): 30μ]. There were mixed 100 g of the silylgroup-containing vinyl copolymer prepared in Reference Example 1, 3 g ofmethyl orthoacetate, 30 g of a mixture of dimethyl succinate, dimethylglutarate and dimethyl adipate (weight ratio of dimethyl succinate:dimethyl glutarate: dimethyl adipate=16.5:66:17) (commercially availablefrom Du Pont Japan Kabushiki Kaisha under the tradename "DBE"), 0.6 g ofdioctyl phosphate and 16.4 g of xylene to give a clear coating. The thusobtained clear coating was sprayed on the steel plate to give a filmhaving a metallic base layer and a clear layer [thickness of the driedfilm of clear coating (clear layer): 50μ]on the plate. After drying thefilm at 23° C. for 7 days, the cross-cut test of the obtained film wasconducted as follows:

The paint film having a size of about 2 cm×about 2 cm was cut in themidde with a razor blade to form a square having a size of about 5mm×about 5 mm. A cellophane adhesive tape having a width of 25 mm wasstuck on the above square and was peeled off. The ratio of the area ofthe clear layer which adhered to the metallic base layer to the wholearea of the square was (from 9 to 10)/10.

EXAMPLE 2

The procedure of Example 1 was repeated except that a CAB-alkyd coatingwas employed as the metallic base [thickness of the dried film (themetallic base layer): 15μ]to give a film having a metallic base layerand a clear layer on the plate. The cross-cut test was conducted in thesame manner as in Example 1.

The ratio of the area of the clear layer which adhered to the metallicbase layer to the whole area of the square was (from 9 to 10)/10.

COMPARATIVE EXAMPLE 1

The procedure of Example 1 was repeated except that xylene was employedinstead of DBE to give a film having a metallic base layer and a clearlayer on the plate. The cross-cut test was conducted in the same manneras in Example 1.

The ratio of the area of the clear layer which adhered to the metallicbase layer to the whole area of the square was 0/10.

COMPARATIVE EXAMPLE 2

The procedure of Example 2 was repeated except that xylene was employedinstead of DBE to give a film having a metallic base layer and a clearlayer. The cross-cut test was conducted in the same manner as in Example1.

The ratio of the area of the clear layer which adhered to the metallicbase layer to the whole area of the square was 5/10.

In addition to the ingredients used in the Examples, other ingredientscan be used in the Examples as set forth in the specification to obtainsubstantially the same results.

What we claim is:
 1. A coating composition comprising:(a) 100 parts byweight of a hydrolyzable silyl group-containing vinyl polymer having onthe main polymer chain end or a side chain thereof at least one silylgroup containing a silicon atom to which a hydrolyzable group is linked,per one polymer molecule, the main chain of said hydrolyzable silylgroup-containing vinyl polymer consisting essentially of a polymer of avinyl monomer; and (b) 0.5 to 100 parts by weight of a dialkyl ester ofa dibasic acid having the formula (1): ##STR4## wherein R¹ is a bivalentgroup having 1 to 10 carbon atoms selected from the group consisting ofalkylene, arylene and aralkylene, R² and R³ are the same or differentand each is an alkyl having 1 to 4 carbon atoms, and n is an integer of1 to
 10. 2. The composition of claim 1, wherein the amount of saiddialkyl ester of a dibasic acid is from 2 to 50 parts by weight per 100parts by weight of said hydrolyzable silyl group-containing vinylpolymer.
 3. The composition of claim 1, further comprising:(c) 0 to 10parts by weight of a curing catalyst for curing said hydrolyzable silylgroup-containing vinyl polymer; and (d) 0 to 10 parts by weight of astabilizer for stabilizing said hydrolyzable silyl group-containingvinyl polymer, said stabilizer being selected from hydrolyzable esters.4. The composition of claim 1, wherein said hydrolyzable silylgroup-containing vinyl polymer is obtained by copolymerizing apolymerizable organic silane and a vinyl monomer.
 5. The composition ofclaim 4, wherein said polymerizable organic silane is selected from thegroup consisting of γ-methacryloyloxypropyltrimethoxysilane,vinyltrimethoxysilane, and vinyltriethoxysilane.
 6. The composition ofclaim 4, wherein said vinyl monomer is selected from the groupconsisting of styrene, esters of acrylic acid, esters of methacrylicacid, acrylamide, acrylonitrile, methacrylamide, N-methyloylacrylamide,maleic anhydride, acrylic acid, methacrylic acid and hydroxylgroup-containing vinyl monomers.